The present invention relates to a sheet cutting apparatus comprising a body; a lower blade provided with a cutting edge and supported on the body; an upper blade provided with a cutting edge and mounted on the body by connecting means so as to be scissorwise movable with respect to the lower blade; as well as support means supported adjacent to the cutting edge of the lower blade below the upper blade.
When operating the sheet cutting apparatus, the upper blade is generally transferred by means of a hydraulic or mechanical system past the generally stationary lower blade tangentially thereto, the blades scissorwise shearing the sheet to be cut. In addition to the cutting effect, such a cutting operation distorts and bends the sheet to be cut. In the scissorwise cutting operation, in which a sheet of metal is sheared against a fixed blade, the article to be cut always bends according to the cutting angle, which causes permanent warpage and distortion to the sheet to be cut.
Efforts have been made to solve the problem of warpage and distortion of the sheet to be cut e.g. by providing a sheet cutting apparatus with a support means fitted adjacent to the cutting edge of the lower blade below the upper blade on its path of travel, the support means being further provided with a leaf spring fitted on top of the support means and being parallel to the cutting blades. The object of the leaf spring is to compress the cut strip of sheet against the upper blade to straighten the distortion caused by cutting. Such sheet cutting apparatus provided with a support means and a corresponding leaf spring are known e.g. from the Swedish Pat. Nos. 362,819 and 369,684 of a company called Intermenua (PYT) Ltd., Johannesburg, South Africa.
A drawback in said known apparatus provided with a support means, particularly in the case of cutters of considerable length, is the use of a pre-stressed leaf spring which causes trouble. A drawback of the leaf spring is that the support force cannot be regulated and equalized over the entire cutting length. A drawback of various support devices is that the required counter-force is too great whereby the counter-force deprives the cutting force, which accomplishes the actual cutting, of some of its effect. Furthermore, these apparatus have not produced satisfactory results, the strips of sheet remain distorted and the straightening is not sufficiently effective.
The object of the invention is to overcome the above drawbacks and to provide a sheet cutting apparatus having no such drawbacks. Particularly, the object of the invention is to develop a more effective receiving, straightening and discharging assembly for sheet cutting equipment.